The study was undertaken to evaluate the adulticidal efficacy of the methanolic leaf extracts and essential oils of Chenopodium ambrosioides, Hyptis suaveolens and Lippia adoensis against adults of Anopheles gambiae. A chemical profile of each plant extracts (qualitative phytochemical screening) and essential oil (GC/MS analysis) was also determined. Doses of 125, 250, 500 and 1000 mg/bottle of plant extracts and 25, 50, 100 and 200 mg/bottle of essential oils were prepared and tested using CDC bottles. In each plant extract, alkaloids, flavonoids, saponins, tannins, phenolic groups, terpenoids, fats and oils were presents. Major chemical constituents of essential oils were thymol (27.09%), sabinene (18.93%) and 4-carene (52.88%) in L. adoensis, H. suaveolens and C. ambrosioides, respectively. L. adoensis extract (at 1000 mg/bottle) and essential oil of H. suaveolens (at 200 mg/bottle) were the most potent causing 100% mortality of An. gambiae adults, 24 h post-exposure. Methanolic extract of L. adoensis (LC50= 20.20 mg/bottle) was the most effective compared to other extracts. Similarly, essential oil of H. suaveolens (LC50= 5.27 mg/bottle) was revealed as the most toxic on An. gambiae adults compared to other oils. Therefore, the extracts of L. adoensis and essential oil of H. suaveolens showed a high activity and should be recommended to be promoting as natural bioinsecticides to control mosquito adults.
Repellency of essential oils of some Kenyan plants against Anopheles gambiae
